(1) Field of the Invention
The invention relates to a cartridge for squeezing-out a cartridge content, in particular a cement, particularly preferably a medical cement, comprising at least one cylindrical hollow space bordered by a cartridge wall, at least one feed plunger that is arranged in the hollow space to be mobile along the cylinder axis of the hollow space and abuts on the cartridge wall, and at least one snap-in means that can be used to lock the feed plunger in place at the cartridge wall.
The invention also relates to a cartridge system having a cartridge of this type as well as a method for dispensing cartridge content, preferably a cement, particularly preferably a medical cement, through the use of a cartridge of said type.
(2) Description of Related Art
Bone cements made of polymethylmethacrylate (PMMA) have been known for decades and are based on the ground-breaking work of Sir Charnley (Charnley, J.: Anchorage of the femoral head prosthesis of the shaft of the femur. J. Bone Joint Surg. 42 (1960) 28-30.). The basic structure of PMMA bone cements has remained the same ever since. PMMA bone cements consist of a liquid monomer component and a powder component. The monomer component generally contains the monomer, methylmethacrylate, and an activator (N,N-dimethyl-p-toluidine) dissolved therein. The powder component consists of one or more polymers that are made by polymerisation, preferably suspension polymerisation, based on methylmethacrylate and co-monomers, such as styrene, methylacrylate or similar monomers, a radio-opaquer, and the initiator, dibenzoylperoxide. Mixing the powder component and the monomer component, a dough that can be shaped plastically is generated by swelling of the polymers of the powder component swell in the methylmethacrylate. Mixing the powder component and the monomer component, the activator, N,N-dimethyl-p-toluidine, reacts with dibenzoylperoxide while forming radicals. The radicals thus formed trigger the radical polymerization of the methylmethacrylate. Upon advancing polymerization of the methylmethacrylate, the viscosity of the cement dough increases until the cement dough solidifies.
Polymethylmethacrylate bone cements can be mixed by mixing the cement powder and the monomer liquid in suitable mixing beakers with the aid of spatulas. This procedure is disadvantageous in that air inclusions may be present in the cement dough thus formed and cause destabilization of the bone cement later on. For this reason, it is preferred to mix bone cement powder and monomer liquid in vacuum mixing systems, since mixing in a vacuum removes air inclusions from the cement dough to a large extent and thus achieves optimal cement quality (Breusch S. J. at al.: Der Stand der Zementiertechnik in Deutschland. Z Orthop. 1999, 137: 101-07). Bone cements mixed in a vacuum have clearly reduced porosity and thus show improved mechanical properties in cured condition.
A large number of vacuum cementing systems has been developed of which the following shall be listed for exemplary purposes: DE 36 40 279 A1, EP 1 020 167 A2, EP 1 016 452 A2, EP 1 005 901 A2, U.S. Pat. Nos. 6,033,105 A, 5,624,184 A, 5,588,745 A, 5,586,821 A, 5,344,232 A, 5,100,241 A, 4,973,168 A, 4,671,263 A, WO 99/67015 A1, WO 94/26403 A1.
A refinement are cementing systems, in which both the cement powder and the monomer liquid are packaged in separate compartments of the mixing systems and are mixed with each other only right before the application of the cement in the cementing system (DE 10 2009 031 178 B3, U.S. Pat. No. 5,997,544 A, EP 0 692 229 A1, U.S. Pat. No. 6,709,149 B1).
In most cementing systems known to date, there is a problem in that, during the mixing, in particular during vacuum mixing of the cement, the feed plunger that can be shifted axially in the cement container needs to be fixed in place, and in that, in contrast, the feed plunger needs to be axially mobile after the mixing in order for the cement dough to be squeezed out due to the axial motion of the feed plunger resulting from the application of pressure on the feed plunger by an applicator gun. Different technical solutions for this problem have been proposed.
EP 0 861 117 A1 discloses a cementing device, in which the feed plunger is secured through a mobile pin that can be pulled out after the cement is mixed such that the plunger thus becomes axially mobile.
DE 43 02 230 A1 describes a cementing device, in which the feed plunger is fixed in place by fins that engages cut-outs in the cartridge floor. Twisting the feed plunger with respect to the cement cartridge twists the fins out of the cut-outs and the feed plunger becomes unlocked.
A totally different fixation of the feed plunger is proposed in WO 02/102287 A1. Here, the feed plunger is connected to the cement container through a breakable connection in such a manner that the feed plunger becomes mobile only by breaking the connection between the feed plunger and the cement container.
EP 2 008 707 A1 describes a closure for a generic cartridge, in which a feed plunger has cut-outs on the outside and a cartridge wall has cut-outs on the inside that are engaged by inside and outside snap-in means of a snap-in ring. The feed plunger is unlocked through the application of an applicator gun and overcoming the snap-in resistance.
This is disadvantageous in that an applicator gun needs to be applied in order to detach the feed plunger. Moreover, the cut-outs are weak sites in the cartridge wall onto which the pressure acts while the cartridge content is being squeezed out, and at which the cartridges might therefore break.